Essential Vocabulary Trait: a specific physical characteristic. ex: seed color Gene: sections of DNA that code for the production of proteins that.

GENETICSTHE SCIENTIFIC STUDY OF

HEREDITY

Essential Vocabulary Trait: a specific physical characteristic. ex: seed color Gene: sections of DNA that code for the production of proteins that

will make a physical trait. Allele: options of what a gene can say. Most genes have at least

two options for alleles. (Reminder: children inherited two of every section of DNA, they could be the same allele or different)

Heterozygous: an individual that has inherited two different alleles for a gene.

Homozygous: an individual that has inherited two of the same alleles for a gene.

True-breeding: individuals who have always produced offspring with the same version of traits as the parent.

Hybrid: individuals who are capable of producing offspring with different versions of a trait from the parent.

Phenotype: physical expression of the genetic information. Genotype: the two forms of genetic information an individual

contains.

History of Genetics Modern genetics was

founded by an Austrian monk named Gregor Mendel.

Mendel was in charge of the garden and decided to use peas to experiment with heredity because peas are small, easy to grow, and produce hundreds of offspring.

Mendel controlled fertilization by picking up pollen with a paint brush and placing it onto the plant to be fertilized.

Mendel’s Experiments

In Mendel’s first experiment he tested the inheritance of one trait (plant height).

Mendel crossed a true breeding tall plant with a true breeding short plant. All of the offspring (F1 generation) were tall.

Mendel allowed the F1 generation to self pollinate and the offspring were ¾ tall and ¼ short (even though the parent was tall).

Mendel’s Experiments Explained Punnett Squares: mathematical diagram that

helps predict the probable outcomes of a cross. Each parent has two sections of DNA for the

trait. Each section is represented by a letter so each parent has two letters.

Dominant versions of a trait are represented by writing the first letter of the version as a capital.

Recessive versions of a trait are represented by writing the same letter except as a lower case.

The two letters are separated and placed on one side of the square as the letters would be separated during meiosis.

The letters from the two parents are combined to make all possible combinations of children. Remember children should have two versions of a trait so two letters.

Simple Inheritance Examples in Humans

Cystic fibrosis- Recessive Trait (CF) is common among white

Americans. 1 in 28 individuals carry the allele and 1 in 2500 babies are born with the disease. A defect in a protein on the plasma membrane causes formation and accumulation of thick mucus in the lungs and digestive track. Physical therapy, diet, and new drugs have extended the life expectancy of these individuals.

Cross a carrier of CF with an individual that has CF. What are the chances the children will have the disease?

Huntington's- Dominant Trait A disorder that results in the

breakdown of areas of the brain. This disorder is lethal. Most of the time dominant alleles with such severe effects (death) would result in death before the individual was old enough to have children preventing the individual from passing the allele on. But Huntington’s does not develop until between the ages of 30 and 50.

Cross a person who is heterozygous for Huntington's with a person who does not have Huntington's. What are the chances the children will have the disease?

Simple Inheritance Examples in Humans

Mendel’s Second Experiment Mendel wanted to know if two traits would

influence each other while being inherited (ex: are all dominant versions of all traits are inherited together?)

To test this Mendel followed two traits through two generations. The first cross was using two true breeding plants to ensure that all of the offspring where heterozygous. Then he allowed these plants to self pollinate.

To create the punnett square remember that each person should have two versions of a trait for each trait (so each person will have 4 letters)

To find the combinations of letters that go on the side of the square (representing the gametes made) FOIL the letters of the parent.

Mendel’s Conclusions Law of dominance: when

more than one allele for a trait exists the trait that is expressed when the two versions are in the same individual is dominant.

Law of segregation: each offspring will inherit only one allele for each trait from each parent.

Law of independent assortment: different traits do not influence the inheritance of each other.

Other Types of Inheritance Mendel studied traits that had two alleles. One

allele was dominant over the other in all of his experiments. In reality not all traits are inherited this way. The pattern of inheritance depends on the trait in question and the resulting phenotypes.

Incomplete Dominance In this inheritance pattern there is

one section of DNA coding for the trait (gene) and there are only two versions (alleles). The difference is in this trait neither of the versions are dominant. This means when the two versions are inherited by one individual, that organism will express a mixture of the two versions and create a third phenotype.

Example: snapdragon flowers can have a red version of DNA or a white version of DNA. When the two versions of DNA are inherited together the resulting color is pink (a mixture of red and white).

Co-dominance In this inheritance pattern there is

one section of DNA coding for the trait (gene) and there are only two versions (alleles). The difference is in this trait both versions are dominant. This means when the two versions are inherited by one individual, that organism will express both versions and create a third phenotype.

Example: Chickens can have DNA for black feathers or DNA for white feathers. If a chicken inherits one piece of each DNA type that chicken will have both black AND white feathers.

Co-dominance Example in Humans Sickle cell

The allele for sickle cells is a mutation of the gene that codes for hemoglobin. This mutation can cause hemoglobin to clump and form long rods giving red blood cells a sickle shape. These cells get stuck in capillaries and cause a lot of pain and deprive tissues of oxygen and nutrients. However, the negative effects are only experienced by individuals who are homozygous for the trait, otherwise there are not enough sickle shaped cells to cause the problems.

There is a good side to this. Being heterozygous or homozygous for the trait makes an individual immune to malaria.

Cross two people who are heterozygous for sickle cell anemia. What are the chances their child will be immune to malaria? What are the chances the child will have the negative side effects of sickle cell disease?

Co-dominance Example in Humans

Multiple Alleles In this inheritance pattern there

is one section of DNA coding for the trait (gene) and there are more than two versions (alleles). Remember that each individual can only inherit two alleles. This inheritance combines simple inheritance with co-dominance. Two of the alleles are co-dominant and if inherited together both will be expressed. The third version of the trait is recessive and will only be expressed if both versions of the trait inherited are recessive.

Multiple Allele Example in Humans Blood Types:

Blood type has three options for alleles: The DNA that codes for the production of A proteins, the DNA that codes for B proteins, and the DNA that codes for no proteins (O).

If the DNA that code for the production of A and B proteins are inherited together, then both proteins are produced and the result is AB blood.

If the DNA that codes for either protein is inherited with the DNA that codes for no proteins the proteins are produced.

Individuals that inherit two sections of DNA that both code for no proteins will have type O blood.

Blood types The proteins on the surface of your blood cells identify your cells

for your body. Your body makes antibodies that attack anything it recognizes as foreign. If you mix the wrong blood types the blood cells will clump together. If this occurs in the body the blood cannot circulate and the person dies.

Sex-linked Traits Remember humans have 23 pairs of

chromosomes. The first 22 pair are called autosomes

and are homologous. The 23rd pair are the sex

chromosomes. If an individual inherits two X chromosomes for the 23rd pair then they are female. If the individual inherits an X and a Y chromosome then they are male.

The X and Y chromosomes do not carry the same genetic information, therefore males inherit only one version of each trait on the X chromosome making it easier for them to inherit and express a recessive trait.

Sex-linked Examples in Humans

Color blindness and hemophilia are recessive traits that are carried on the X chromosome. If an individual inherits two X chromosomes then they can be heterozygous or a carrier and not express the recessive trait.

Polygenic Traits In this inheritance pattern there

are many section of DNA coding for the trait (genes) and there can be more than two versions (alleles) for each gene. The expression of the trait depends on how many dominant and recessive versions are inherited creating a range of phenotypes. This type of inheritance cannot be represented in a punnett square, it is represented by a bell curve graph.

Example: Human hair color, eye color, height, and skin color

Karyotypes A picture of the chromosomes of a person. This allows us to

identify gender and any chromosomal mutations. A human mutation identified using a karyotype is Down

syndrome. This is a mutation where an individual inherits three of the 21st chromosome causing mental retardation and physical abnormalities.

Pedigree This is a graphic representation of a family tree identifying genders, relationship, and which individuals posses the trait in question.

Using a pedigree it is sometimes possible to determine the inheritance pattern of the trait in question.

Note that polygenic traits cannot be followed using a pedigree.

Copy the information in the top left picture onto the bottom of your notes. Also include that generations are represented by roman numerals while individuals within a generation are assigned aerobic numbers.

Environmental Influences Genetic information is not the only

contributing factor to the phenotype or appearance of an organism. The environment can sometimes determine when and how genetic information is expressed.

Internal conditions (such as other traits and changes in hormone levels caused by age, proper diet, and exercise) can control when traits are expressed. Examples include: Blond hair when you were young and

dark hair when older. Proper diet and exercise can

decrease the chances of developing diabetes and heart disease even if you are genetically predisposed.

The external environment can also play a role in the expression of certain traits. Examples include: Temperatures determining the

coat color of arctic foxes. Smoking increases the expression

of lung cancer. Sun exposure as well as vitamin

D and folic acid deficiency can cause skin cancer to be expressed.

Proper diet limits the effects of PKU, a genetic disorder in which dairy can cause severe brain damage. If the individual is not exposed to dairy then they do not develop brain damage.

***PKU is a recessive trait***

Environmental Influences